CN103521256B - Molecular sieve catalyst for catalyzing and dehydrating glycerin to prepare acraldehyde and preparation method of molecular sieve catalyst - Google Patents

Abstract

The invention belongs to the technical field of chemistry and chemical engineering, and specifically relates to a molecular sieve catalyst for catalyzing the dehydration of glycerin to prepare acrolein and a preparation method thereof. The catalyst of the invention is ZSM-5 molecular sieve containing mesoporous, and HY, Hβ, ZSM-11 molecular sieve containing mesoporous. The preparation method is to stir the corresponding microporous molecular sieve in an alkali solution of a certain concentration and a certain temperature for a period of time, filter, wash and dry, carry out NH ₄ NO ₃ ion exchange, and roast at a high temperature after drying to obtain the catalyst. The preparation process of the invention is simple, and the prepared catalyst greatly improves the conversion rate of glycerin and the stability of the catalyst while maintaining high acrolein selectivity. The catalyst precursor of the invention has wide source, cheap price, low production cost, prolongs the service life of the catalyst after modification, has high catalytic activity, can regenerate the catalyst, has little corrosion to equipment, and reduces environmental pollution.

Description

Molecular sieve catalyst for catalyzing glycerin dehydration to prepare acrolein and preparation method thereof

technical field

The invention belongs to the technical field of chemistry and chemical engineering, and in particular relates to a catalyst used in the high-value conversion of biodiesel by-product glycerin and a preparation method thereof, in particular to a molecular sieve catalyst for catalyzing the dehydration of glycerin to prepare acrolein and a preparation method thereof .

Background technique

The energy crisis has caused countries to look for new energy sources that can replace fossil energy sources. Among them, biodiesel has become one of the very promising alternatives due to its low-carbon, environmentally friendly and renewable. All countries in the world have formulated and used biodiesel incentive policies, which has led to a rapid increase in biodiesel production. Subsequently, the production of its by-product glycerin has greatly increased and the price has dropped sharply. Therefore, finding a high-value conversion route for glycerol has become a research hotspot in the world.

Among the various utilization methods of glycerol, acrolein, the product of glycerol dehydration, is a very important chemical intermediate, which can further produce high-value compounds such as acrylic acid and DL-methionine that have important industrial and agricultural values and are in short supply. At present, acrolein is mainly produced by the selective oxidation of propylene, but the depletion of petroleum resources and the rise of international oil prices have caused the price of raw material propylene to remain high, increasing the production cost of acrolein and its downstream product acrylic acid. Therefore, it has very high economic value to prepare acrolein with a large amount of cheap glycerol.

Patent WO 2006087083 discloses that ZSM-5 and β zeolite are used as catalysts for glycerin dehydration, and the accumulative feed of 16 g glycerol yields conversions of 79% and 99%, with yields of 39.1% and 56.9%, respectively.

Patent CN 101070276A reports that glycerin is on acidic zeolite, under the conditions of temperature 200-500 ℃, pressure 0.001-3.0 MPa and liquid space velocity 0.1-100 h ^-1 , the conversion rate of glycerin is not high, and acrolein The selectivity of the catalyst is very low, and the by-products are more and are easily adsorbed on the catalyst, causing the carbon on the surface of the catalyst to reduce the reactivity.

Patents US 5426249 and CN 1034803C disclose phosphoric acid catalysts supported by alumina, ZSM-5, HY, etc., the conversion rate of glycerol is 19%, and the selectivity of acrolein is about 71%. Although the selectivity of acrolein is high, the conversion of glycerol is very low.

In the above reports, although the acidic zeolite has attracted more attention as a catalyst for the dehydration of glycerol to acrolein, the catalyst deactivates quickly because the reaction is very easy to form carbon deposits to block the active sites of the catalyst. If the mesoporous molecular sieve catalyst can be synthesized, its stability will be greatly improved. Alkali treatment desiliconization technology is a method with low economic cost, which can introduce mesopores into zeolite on a large scale and establish a multi-level pore system. However, the alkali treatment method reported in the literature has a relatively wide distribution of mesopore diameters, and the strength of the catalyst decreases significantly after treatment. Through a lot of research, we found that the alkali concentration has a great influence on the introduction of mesopores, and a single concentration of alkali treatment cannot obtain a catalyst with a narrow pore size distribution and high structural strength. The invention introduces mesopores into ZSM-5 by adopting two-step alkali treatment with a specific concentration to obtain a mesoporous zeolite with low mass transfer resistance, stable structure and large-scale production, and is successfully applied in the reaction of glycerin dehydration. Similar results have not been reported.

Contents of the invention

The object of the present invention is to provide a molecular sieve catalyst for catalyzing the dehydration of glycerin to prepare acrolein, which is simple in preparation, suitable for large-scale production, and good in catalytic stability, and a preparation method thereof.

The molecular sieve catalyst used to catalyze the dehydration of glycerin to prepare acrolein provided by the invention is an acidic ZSM-5 molecular sieve containing both micropores and mesoporous channels.

The acidic molecular sieve catalyst used to catalyze the dehydration of glycerin to prepare acrolein includes HY, Hβ and ZSM-11 molecular sieves containing micropores and mesoporous channels.

The mesoporous acidic molecular sieve catalyst of the present invention can be prepared by an alkali dissolution method, and the specific steps are:

(a) Pretreatment, stirring various industrial acidic zeolite molecular sieves in 0.01 M-0.02 M alkali solution at 40-60 °C for 12 h-24 h;

(b) Stir various pretreated industrial acidic zeolite molecular sieves in 0.1 M-0.4 M alkali solution at 65-85 °C for 0.5 h-5 h;

(c) Suction filtration, washing until PH = 7, and then drying in an oven at 60-140°C for 12-24 hours;

(d) Ion exchange 3-4 times in 0.18-2.2 M ammonia solution, 4-6 hours each time;

(e) Dry in an oven at 60-140 °C for 12-24 h;

(f) Calcining the catalyst at 550-600°C for 6-12 hours to obtain the catalyst of the present invention.

In the present invention, the silicon-aluminum molar ratio of the molecular sieve is between 25 and 100, the alkali solution is one of sodium hydroxide and potassium hydroxide, and the ammonium solution is one of ammonium nitrate and ammonium chloride; The ratio of molecular sieve and alkali solution is 20-30 ml per gram, and the ratio of molecular sieve and ammonium solution is 8-12 ml per gram (preferably 10 ml per gram).

Figure 1 is the XRD pattern of the catalyst before and after modification, and the results show that the MFI structure and crystallinity of ZSM-5 have not changed. Figure 2 is the N ₂ adsorption curves of the catalyst before and after modification. The modified catalyst obviously has a hysteresis loop when the relative pressure is greater than 0.4 MPa, indicating that a large number of irregular slit-type mesopores are formed. . The results of pore size distribution show that the size of the generated mesopores is around 5-20 nm. Figure 3 is the TEM image of the catalyst before and after modification. From the figure, the change of the catalyst structure and the newly formed mesopores before and after alkali treatment can be seen more clearly and intuitively.

In the present invention, under the mesoporous acidic ZSM-5 catalyst, the raw materials enter the fixed bed reaction at a certain speed through the pump, wherein the reaction conditions for the preparation of acrolein by dehydration of glycerin are: catalytic reaction temperature: 280-360 ° C, pressure: 1 atmospheric pressure, glycerol concentration 20%~50%, liquid hourly space velocity 1.2 h ^-1 ~4.8 h ^-1 . The product was manually sampled every hour and then analyzed by gas chromatography using a WAX column and FID detector. The analysis conditions were 80 °C for 2 min, 20 °C was raised to 250 °C every minute, and maintained for 10 minutes.

The amount of mesopores introduced and the size of mesopores have a significant impact on the catalytic activity. The catalyst prepared at 85 ℃ for 0.5 h has high catalytic activity and stability, the conversion of glycerin after 10 h at 320 ℃ and liquid hourly space velocity of 2.4 h ^-1 is 93%, and the selectivity of acrolein 78%. The conversion rate of glycerol was 69% and the selectivity of acrolein was 79% for the unmodified commercial ZSM-5 catalyst at 5 h.

The catalyst of the invention is characterized in that the preparation of the catalyst is simple and suitable for large-scale production; the catalyst has good stability and high practical value.

Description of drawings

Figure 1 is the XRD pattern of the catalyst before and after modification.

Figure 2 shows the _N adsorption curves of catalysts before and after modification.

Figure 3 is the TEM image of the catalyst before and after modification.

Detailed ways

The present invention is further described below by way of examples.

Example 1

The meso-ZSM-5-at65 catalyst is prepared as follows:

Weigh 5 g of industrial ZSM-5 catalyst, stir in 0.01 M NaOH solution at 45 °C for 12 h, and filter with suction. The filter residue was stirred in 0.2 M NaOH solution at 65 °C for 0.5 h. Then filter and wash until neutral, and ventilate and dry at 80 °C. Ion exchange in 0.2 M NH ₃ NO ₃ 3 times, 5 h each time. Filter and wash until neutral, and ventilate and dry at 80 °C. After the dry mixture is obtained, it is heated and roasted in a muffle furnace at a heating temperature of 550 °C. The firing time is 6 h.

0.5 g of the prepared meso-ZSM-5-at65 catalyst is packed into a reaction tube with a diameter of 8 mm, and 20% aqueous glycerin solution is injected into the reaction tube with a pump at a speed of 0.1 ml/min, and the reaction temperature is 320 °C, and the pressure of the reaction system was 1 atmosphere. After 10 h, the conversion rate of glycerol was 93%, and the selectivity of acrolein was 75%; after 24 h, the conversion rate of glycerol was 67%, and the selectivity of acrolein was 73%.

Example 2

The meso-ZSM-5-at85 catalyst is prepared as follows:

Weigh 5 g of industrial ZSM-5 catalyst, stir in 0.01 M NaOH solution at 45 °C for 12 h, and filter with suction. The filter residue was stirred in 0.2 M NaOH solution at 85 °C for 0.5 h. Then filter and wash until neutral, and ventilate and dry at 80 °C. Ion exchange in 0.2 M NH ₃ NO ₃ 3 times, 5 h each time. Filter and wash until neutral, and ventilate and dry at 80 °C. After the dry mixture is obtained, it is heated and roasted in a muffle furnace at a heating temperature of 550 °C. The firing time is 6 h.

0.5 gram of the prepared meso-ZSM-5-at85 catalyst is packed into a reaction tube with a diameter of 8 mm, and 20% glycerin aqueous solution is injected into the reaction tube with a speed of 0.1 ml/min with a pump, and the reaction temperature is 320 °C, and the pressure of the reaction system was 1 atmosphere. After 10 h, the conversion rate of glycerol was 93%, and the selectivity of acrolein was 78%; after 35 h, the conversion rate of glycerol was 71%, and the selectivity of acrolein was 74%.

Example 3

The meso-ZSM-5-at85 catalyst is prepared as follows:

Weigh 5 g of industrial ZSM-5 catalyst, stir in 0.01 M NaOH solution at 45 °C for 12 h, and filter with suction. The filter residue was stirred in 0.2 M NaOH solution at 75 °C for 1 h. Then filter and wash until neutral, and ventilate and dry at 80 °C. Ion exchange in 0.2 M NH ₃ NO ₃ 3 times, 5 h each time. Filter and wash until neutral, and ventilate and dry at 80 °C. After the dry mixture is obtained, it is heated and roasted in a muffle furnace at a heating temperature of 550 °C. The firing time is 6 h.

0.5 g of the prepared meso-ZSM-5-85 catalyst is packed into a reaction tube with a diameter of 8 mm, and 20% glycerin aqueous solution is injected into the reaction tube with a pump at a speed of 0.1 ml/min, and the reaction temperature is 280 °C, and the pressure of the reaction system was 1 atmosphere. After 10 h, the conversion rate of glycerol was 43%, and the selectivity of acrolein was 81%.

Example 4

The meso-ZSM-5-at85 catalyst is prepared as follows:

Weigh 5 g of industrial ZSM-5 catalyst, stir in 0.01 M NaOH solution at 45 °C for 12 h, and filter with suction. The filter residue was stirred in 0.2 M NaOH solution at 85 °C for 2 h. Then filter and wash until neutral, and ventilate and dry at 80 °C. Ion exchange in 0.2 M NH ₃ NO ₃ 3 times, 5 h each time. Filter and wash until neutral, and ventilate and dry at 80 °C. After the dry mixture is obtained, it is heated and roasted in a muffle furnace at a heating temperature of 550 °C. The firing time is 6 h.

0.5 g of the prepared meso-ZSM-5-at85 catalyst is packed into a reaction tube with a diameter of 8 mm, and 20% aqueous glycerin solution is injected into the reaction tube with a pump at a speed of 0.1 ml/min, and the reaction temperature is 360 °C, and the pressure of the reaction system was 1 atmosphere. After 10 h, the conversion rate of glycerol was 100%, and the selectivity of acrolein was 75%.

Example 5

The meso-ZSM-5-at85 catalyst is prepared as follows:

Weigh 5 g of industrial ZSM-5 catalyst, stir in 0.01 M NaOH solution at 45 °C for 12 h, and filter with suction. The filter residue was stirred in 0.2 M NaOH solution at 85 °C for 5 h. Then filter and wash until neutral, and ventilate and dry at 80 °C. Ion exchange in 0.2 M NH ₃ NO ₃ 3 times, 5 h each time. Filter and wash until neutral, and ventilate and dry at 80 °C. After the dry mixture is obtained, it is heated and roasted in a muffle furnace at a heating temperature of 550 °C. The firing time is 6 h.

0.5 g of the prepared meso-ZSM-5-at85 catalyst is packed into a reaction tube with a diameter of 8 mm, and 20% aqueous glycerin solution is injected into the reaction tube with a pump at a speed of 0.05 ml/min, and the reaction temperature is 320 °C, and the pressure of the reaction system was 1 atmosphere. After 10 h, the conversion rate of glycerol was 100%, and the selectivity of acrolein was 79%.

Example 6

The meso-ZSM-5-at85 catalyst is prepared as follows:

Weigh 5 g of industrial ZSM-5 catalyst, stir in 0.01 M NaOH solution at 45 °C for 12 h, and filter with suction. The filter residue was stirred in 0.2 M NaOH solution at 85 °C for 0.5 h. Then filter and wash until neutral, and ventilate and dry at 80 °C. Ion exchange in 0.2 M NH ₃ NO ₃ 3 times, 5 h each time. Filter and wash until neutral, and ventilate and dry at 80 °C. After the dry mixture is obtained, it is heated and roasted in a muffle furnace at a heating temperature of 550 °C. The firing time is 6 h.

0.5 g of the prepared meso-ZSM-5-at85 catalyst is packed into a reaction tube with a diameter of 8 mm, and 20% aqueous glycerin solution is injected into the reaction tube with a pump at a speed of 0.2 ml/min, and the reaction temperature is 320 °C, and the pressure of the reaction system was 1 atmosphere. After 10 h, the conversion rate of glycerol was 63%, and the selectivity of acrolein was 78%.

Example 7

The meso-HY-at85 catalyst is prepared as follows:

Weigh 5 g of industrial HY catalyst, stir in 0.01 M NaOH solution at 45 °C for 12 h, and filter with suction. The filter residue was stirred in 0.2 M NaOH solution at 85 °C for 0.5 h. Then filter and wash until neutral, and ventilate and dry at 80 °C. Ion exchange in 0.2 M NH ₃ NO ₃ 3 times, 5 h each time. Filter and wash until neutral, and ventilate and dry at 80 °C. After the dry mixture is obtained, it is heated and roasted in a muffle furnace at a heating temperature of 550 °C. The firing time is 6 h.

0.5 g of the prepared meso-HY-at85 catalyst was packed into a reaction tube with a diameter of 8 mm, and 20% glycerol aqueous solution was injected into the reaction tube with a pump at a speed of 0.1 ml/min, and the reaction temperature was 320 ° C. The pressure of the reaction system was 1 atmosphere. After 10 h, the conversion rate of glycerol was 54%, and the selectivity of acrolein was 57%.

Example 8

The meso-Hβ catalyst was prepared as follows:

Weigh 5 g of industrial Hβ catalyst, stir in 0.01 M NaOH solution at 45 °C for 12 h, and filter with suction. The filter residue was stirred in 0.2 M NaOH solution at 85 °C for 0.5 h. Then filter and wash until neutral, and ventilate and dry at 80 °C. Ion exchange in 0.2 M NH ₃ NO ₃ 3 times, 5 h each time. Filter and wash until neutral, and ventilate and dry at 80 °C. After the dry mixture is obtained, it is heated and roasted in a muffle furnace at a heating temperature of 550 °C. The firing time is 6 h.

0.5 g of the prepared meso-Hβ-at85 catalyst was packed into a reaction tube with a diameter of 8 mm, and 20% glycerol aqueous solution was injected into the reaction tube with a pump at a speed of 0.1 ml/min, and the reaction temperature was 320 ° C. The pressure of the reaction system was 1 atmosphere. After 10 h, the conversion rate of glycerol was 68%, and the selectivity of acrolein was 64%.

Claims (4)

1. A preparation method of a molecular sieve catalyst used to catalyze glycerin dehydration to prepare acrolein, the catalyst is an acidic ZSM-5 molecular sieve containing both micropores and mesoporous channels, or HY, Hβ, ZSM-5 containing mesoporous 11 molecular sieves, and the mesopore diameter is 5-20 nm; It is characterized in that the specific steps are: (a) Pretreatment, stirring acidic zeolite molecular sieves in 0.01 M-0.02 M alkali solution at 40-60 °C for 12 h-24 h; (b) Stir the pretreated acidic zeolite molecular sieve in a 0.1 M-0.4 M alkali solution at 65-85 °C for 0.5 h-5 h; (c) Suction filtration, washing until PH = 7, and then drying in an oven at 60-140°C for 12-24 hours; (d) Ion exchange 3-4 times in 0.18-2.2 M ammonium solution, 4-6 hours each time; (e) Dry in an oven at 60-140 °C for 12-24 h; (f) Calcining at 550-600°C for 6-12 hours to obtain the catalyst. 2. The preparation method according to claim 1, characterized in that: the silicon-aluminum ratio of the molecular sieve is between 25 and 100. 3. The preparation method according to claim 1, characterized in that: the alkali solution in the steps (a) and (b) is one of sodium hydroxide and potassium hydroxide, and the ratio of molecular sieve to alkali solution is Gram 20-30ml. 4. preparation method according to claim 1 is characterized in that: described ammonium solution is a kind of of ammonium nitrate, ammonium chloride; The ratio of molecular sieve and ammonium solution is every gram 8-12 ml.